Lazy load Properties::isDrawingEnabled.

Properties::isDrawingEnabled can unexpectedly return true
even if the system property debug.hwui.drawing_enabled is false,
if its called before RenderThread is created.

This commit changes the underlying logic to lazy load the
debug.hwui.drawing_enabled prop value.

Bug: 201691826
Test: m
Change-Id: I599426c8734d418f073fd0456c2b1149fb69d80c